It is invalid, you need at least two vector entries for an initial SP and PC at 0x08000000, they can point anywhere.

>>Can the applications be run only from start of flash?

Correct. Or more technically address zero, where FLASH, RAM or ROM is initially shadowed via the BOOTx pin settings. In the normal case 0x08000000 content is readable at 0x00000000, and SCB->VTOR resets to zero.